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4th Gen ('81-'88): 1987 Monte SS low speed running issue

  #1  
Old 09-11-2018, 07:18 AM
Thread Starter
Join Date: Sep 2018
Posts: 1
Default 1987 Monte SS low speed running issue

I have a 1987 Monte Carlo SS, a 44,000 mile survivor car which was original except battery, tires and muffler/tailpipes. About a year after buying it, it developed what I will call a random miss. This miss does not happen every revolution or at full throttle, so ruled out a mechanical issue. At wide open throttle with the engine pulling hard, there is no evidence of the issue, but as soon as I come down into running on the primary circuit, the miss is back and is felt as a lunge in the drivers seat. While at idle and through RPM range, you can see the motor shake with the miss. What I have yet to be able to determine is whether it is fuel or ignition related. I have put the car into open loop mode to verify it actually goes into closed loop. I started with replacing the common tune up items and eventually went to the shot gun approach. Here is what I have done or replaced over the last 2 years: Set "base timing", plugs, plug wires, cap and rotor, new distributer and pickup coil, ignition module, coil, ECM from a known good running car, professionally rebuilt OEM carb, replacement carb off eBay, intake manifold gasket, O2 sensor, ran with vacuum port plugged, EGR valve, knock sensor, MAP, BAP, spark control module. The thing is, none of these new parts changed the problem (better or worse). I have the factory manual and supplement and have read them. As I replaced sensors, I checked wiring and connectors and found nothing out of place. I have checked the grounds and as a 100% rust free car, they all looked and ohmed out good.
So I am at my wits end with the car and thought I would try here to see if anyone else has experienced this or if one of you has more experience with the CCC and electronic Qjet systems and might have an idea.
Thanks
Greg
 
  #2  
Old 09-11-2018, 08:02 AM
Join Date: Nov 2017
Location: Isanti, MN
Posts: 774
Default

Sounds like you have tried about everything , it does sound like a ignition problem to me. One test you could try if you can get the car in a garage or a shaded area, use a spray bottle and spray down the wires and cap . Look and listen for a wire arcing to a ground , usually helps if someone can put it under load while you look. Even tho you have new parts maybe there's a crack in the porcalin on the plug or arcing on the cap that you cant see. Hoping you used AC delco plugs .Another possibility could be the shaft on the distributor is getting worn and moving around too much. You didn't give us any engine info so I'll assume you have a V8 since you mentioned the famous Q jet. Maybe others will have idea's for you also. Good luck
 

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